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Kumquat and calamondin are two small-size citrus fruits. Owing to their health benefits, they are traditionally used as folk medicine in Asian countries. However, the research on flavonoids and biological activities of kumquat and calamondin have received less attention. This review summarizes the reported quantitative and qualitative data of phenolic compositions in these two fruits. Effects of maturity, harvest time, various solvent extractions and heat treatment of phenolic compositions, and bioactivities were discussed; distributions of the forms of phenolic compounds existing in kumquat and calamondin were also summarized. Furthermore, biological activities, including antioxidant, antityrosinase, antimicrobial, antitumor, and antimetabolic disorder effects, have also been discussed. Effective phenolic components were proposed for a certain bioactivity. It was found that C-glycoside flavonoids are dominant phenolic compounds in kumquat and calamondin, unlike in other citrus fruits. Up to now, biological activities and chemical characteristics of C-glycoside flavonoids in kumquat and calamondin are largely unknown.

Calamondin has been demonstrated to exhibit antioxidant function and tyrosinase inhibitory activity, which might be attributed to its flavonoid compounds. To improve their application, the flavonoid compositions and antioxidant activity of calamondin extracts, prepared by different solvents, were investigated. The results showed that total phenolic and flavonoid contents of extracts from peel of calamondin were higher than that from pulp, except the flavonoid content in hot water extract. The flavonoids found in extracts of calamondin were 3',5'-di-C-β-glucopyranosylphloretin (DGPP), naringin, hesperidin, nobiletin, tangeretin, and diosmin. DGPP exhibited the highest quantity, while naringin and hesperidin were the other two major flavonoids. The content of DGPP in hot water extract of peel was higher than in extracts of organic solvents, however, the contents of nobiletin and tangeretin were found only in extracts of organic solvents. The highest levels of total flavonoids and DGPP were obtained in hot water extract from peel at 90°C. The extracts of hot water and ethyl acetate showed higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging potency than that of ethanol and methanol. A positive relationship existed between total phenolic contents and DPPH scavenging potency (p < 0.01), while total flavonoid compositions also showed correlation (p < 0.05). Thus, DGPP, naringin, and hesperidin might contribute to antioxidant activity. Collectively, the hot water extract of calamondin peel might have potential for health food and cosmetic applications due to its good antioxidant activity and high level of DGPP.

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In grass shrimp (Penaeus monodon), the combined total content of the uricogenic bases adenine (Ade) and hypoxanthine (Hyp) decreased gradually during storage. Whether stored at 5ЊC or at room temperature (22ЊC), a negative regression of log Ade and a positive regression of the Kp value (Hyp/Ade) were observed. Volatile basic nitrogen (VBN) increased during storage at 5ЊC and 22ЊC. Correlations between the content of log Ade and VBN at 5ЊC and 22ЊC were Ϫ0.9248 (pϽ0.01) and Ϫ0.8139 (pϽ0.05, while those between the Kp value and VBN were 0.9557 (pϽ0.001) and 0.8197 (pϽ0.05), respectively. At the point where the shrimp would remain acceptable, the upper limits of Kp were 1.42 and 1.29 for storage at 5ЊC and 22ЊC, respectively; the corresponding lower limits of Ade were 18.72 and 20.42 mole/g dry wt.to the flask. This solution was then filtered through a 0.2 m membrane filter. The purine bases were separated by HPLC using a reversed phase column (Lichrospher 5C 18 , 250 ϫ 4 mm, i.d., Merck, Germany) with 0.02M KH 2 PO 4 buffer, pH 3.2. The eluate was passed through a UV detector at 254 nm and the concentrations of the purine bases, Ade, Hyp, guanine (Gua) and xanthine (Xan) were computed automatically on the basis of peak areas. The purine standards were obtained from Sigma Chemical Co., (St. Louis, MO). Our new proposed Kp value was calculated from the ratio of hypoxanthine/ adenine. All values were computed on the basis of mole/g dry weight.

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